Lipoteichoic acids (LTAs) are a group of amphipathic substances found in the cell wall of gram-positive bacterial extending from the outer cell membrane through the cell wall to the surface. The main group of LTAs consists of a hydrophilic poly(glycerophosphate) backbone and a hydrophobic glycolipid moiety. The hydrophilic backbone may be substituted with alanine, hexoses and hexosamines. The glycolipids described so far were mainly dihexosylglycerols and some trihexosylglycerols. Lipoteichoic acids show genus and species variation in the degree of polymerization of the hydrophilic chain, in the nature and degree of glycosidic substitution, in the extent of D-alanyl ester substitution, and in the structure of the lipid moiety (A. J. Wicken et al., Science, 187, 1161-1167, (1975), and Microbiology, 360-365, (1977); Fischer W., Physiology of lipoteichoic acids in bacteria. Adv. Microb. Physiol., 29(233): 233-302 (1988), Fischer W., Mannsfeld T., Hagen G., On the basic structure of poly-(glycerophosphate) lipoteichoic acids, Biochem. Cell Biol., 68(1): 33-43, (1990).
LTAs have been reported as having antitumor activity (EP 135 820; U.S. Pat. No. 4,678,773; A. Yamamoto et. al. 1985, Br. J. Cancer, 51, 739-742; and H. Usami et. al., Br. J. Cancer, 1988, 57, 70-73).
LTAs were isolated from e. g. Lactobacillus helveticus (NCIB 8025), Lactobacillus fermenti (NCTC 6991), Streptococcus faecalis, 39, Streptococcus lactis (ATCC 9936), Streptococcus mutans, AHT (A. J. Wicken et al, 1975), and Streptococcus pyogenes SV strain (ATCC 21059) (EP 135 820, U.S. Pat. No. 4,678,773, H. Usami et. al. 1985).
A streptococcal acid glycoprotein (SAGP) with antitumor activity was isolated by M. Kanaoka et. al., Jp. J. Cancer Res. (Gann), 78, 1409-1414, (1987) from the low virulent strain Streptococcus pyogenes Su ATCC 21060. OK-432, a cell preparation from said strain, has found clinically use as an antitumor agent. However, in the meantime it was withdrawn from the market.
The LTAs described up to now carried more than one monosaccharide in the glycceroglycolipid anchor. Different glycolipid structures have been described by Fischer et al. 1988 and 1990.
An LTA with a monohexosylidiacylglyceroglycolipid as lipid anchor has not been described so far.